Plunger to Form a Liquid Ring to Seal Against Gas Bypass

ABSTRACT

A plunger for moving up and down in a tubing string in a plunger lift system includes an elongated body having an upper end, a lower end and a longitudinal axis, an upper passage extending axially in the body from a top opening located toward the upper end, and a liquid cross-hole extending from the upper passage to an outer circumferential surface of the body. The upper passage is closed to the exterior of the lower end at least when the plunger is located at or proximate to the bottom end of the tubing string. In some embodiments the upper passage extends from the top opening to a terminal end or position located inside the body and not in communication with the exterior of the lower end. The upper passage may extend from the top opening to a bottom opening toward the lower end and include a valve element to selective close the bottom opening.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62/301,237, filed Feb. 29, 2016, which is incorporated herein by reference in its entirety as if fully set forth herein.

BACKGROUND

This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.

Hydrocarbon producing gas wells generally produce liquids in addition to the flowing gas stream. These fluids, gas and liquids, are conducted to the surface by a string of production tubing that communicates the below ground formation to piping system at the surface. Removal of the liquid fraction of the fluid column is mandatory for maintaining the unrestricted production of gas from the production zone formation. Frequently, a beam pump unit is employed for this task. However, beam pumping units are expensive and suffer from high maintenance costs.

In the field of plunger lift, a plunger acts as an unattached piston within the length of the production tubing for the purpose of lifting liquids from an active, gaseous hydrocarbon-bearing formation. In the life cycle of a plunger lift system, the plunger travels first downwardly to the bottom region of the tubing string adjacent to the formation then upwardly within the tubing string multiple times within the course of the day. The use of a plunger within the tubing conduit of a gas well will enable the upward flow of light-density gas to push toward the surface those heavier liquids within the tubing string.

Plunger movement is controlled by one or more flow control valves located between the upper end of this tubing conduit and the surface piping arrangement. Whenever a flow control valve at the surface is closed, the flow of fluids from the near-surface wellbore is terminated. At this point and by the force of gravity, the plunger within the tubing falls to the bottom of the production string within the well bore where it typically encounters a shock-spring arrangement approximate the end of the tubing string. As the plunger falls, it encounters gas and liquid within the tubing. Being lighter relative to the plunger, these fluids are displaced around the plunger to a position above the falling plunger device. This migration is made possible by the undersized dimension of the piston-like plunger. In bypass plungers the gas and liquid migrate up through an open central passageway within the plunger during descent of the plunger in the wellbore.

Later, once flow is reestablished at the surface, a plunger will begin its return to its uppermost range at the upper end of the tubing string. A plunger is forced to the surface by the up-flowing gas stream below it. As the plunger migrates upwardly, it pushes to the surface any liquid above the plunger and ahead of the gas column that is expanding from below the plunger.

There exist three plunger styles, the solid one-piece plunger (non-bypass), the bypass plunger with an internal valve element and the two-piece bypass plunger. The effectiveness of each of these plungers is a function of its sealing element. The sealing elements of the several plunger iterations within the art vary in design and efficiency. There exist two common and one less common external sealing mechanism, the spiral groove design, the pad sealing element and the less common elastomeric sealing elements. Any of these three sealing means can be used in conjunction with any of the three plunger styles.

A two-piece plunger will not return toward the surface until it first comes into contact with and joins to its external valve element, generally a spherical ball. Classified as one-piece plungers, both the dart plunger and the captured rod plunger have an internal valve element that is shifted into the closed position as the plunger reaches the bottom spring stop arrangement adjacent the end of the tubing. Once this internal valve is shifted to a closed position, these bypass style plungers will return to the surface, carried by the up-flowing gas stream.

The common spiral plunger is a solid one-piece plunger body that does not have an internal passageway extending the length of the body (i.e., bypass). The common spiral plunger typically has concentric grooves arrayed along its length that serve to retard the flow of gas from below the plunger. The solid one-piece plunger fits within the tubing string somewhat loosely per the requirements specified within the industry. The industry standards ensure that the purposefully undersized plunger will not become lodged within the tubing string. The pad style plunger and its sealing element fit more snugly within the tubing string and constitute a superior seal as compared to the spiral plunger. Because the sealing elements of the pad plunger are biased outwardly by springs, the larger pad plunger will not become wedged within the tubing.

A spiral plunger is also referred to as a bar-stock plunger based on its simplicity and ruggedness. The captured-rod plunger, the dart-style plunger and the padded plunger are more complex, efficient, costly and less robust than the common spiral plunger. The choice of plungers is predicated on cost versus efficiency while the complexity of use is weighed as a factor, as well. Of the available plungers, the spiral plunger is low cost and simple to use but judged inefficient. Examples of bar-stock plungers utilizing concentric grooves as inefficient sealing means to retard gas flow across the plunger from below are disclosed in U.S. Pat. Nos. 4,410,300 and 4,502,843.

SUMMARY

A plunger for moving up and down in a tubing string in a plunger lift system includes an elongated body having an upper end, a lower end and a longitudinal axis, an upper passage extending axially in the body from a top opening located toward the upper end, and a liquid cross-hole extending from the upper passage to an outer circumferential surface of the body. The upper passage is closed to the exterior of the lower end at least when the plunger is located at or proximate to the bottom end of the tubing string. In some embodiments the upper passage extends from the top opening to a terminal end or position located inside the body and not in communication with the exterior of the lower end. The upper passage may extend from the top opening to a bottom opening toward the lower end and include a valve element to selective close the bottom opening.

The liquid cross-hole may extend radially from the upper passage, tangentially from the upper passage. In some embodiments, the body may have a plurality of liquid cross-holes one or more radially and/or tangentially from the upper passage. The one or more liquid cross-holes may extend substantially perpendicular to the longitudinal axis and/or at downward or upward angles.

In some embodiments a plurality of liquid cross-holes are arranged circumferentially and axially on the body. An array of liquid cross-holes may be spaced circumferentially apart along the same horizontal plane. In one or more embodiments an array of at least three liquid cross-holes are arranged on substantially the same horizontal plane and substantially equally spaced apart. Each liquid cross-hole of an array of liquid cross-holes may extend substantially perpendicular to the longitudinal axis or at an upward or downward angle. In some embodiments an additional liquid cross-hole may be spaced axially from an array of liquid cross-holes on a horizontal plane and wherein the additional liquid cross-hole extends tangentially from the upper passage.

In accordance to embodiments the plunger includes a sealing mechanism located on the outer circumferential surface, such as and not limited to one or more circumferential grooves or ribs, pads, and elastomeric elements.

A method, for example of operating a plunger lift system or producing a fluid from a wellbore, includes locating a plunger proximate a bottom end of a tubing that is disposed in a wellbore, the plunger having an elongated body having an upper end, a lower end and a longitudinal axis, an upper passage extending axially in the body from a top opening located toward the upper end, and a liquid cross-hole extending from the upper passage to an outer circumferential surface of the body; ascending the plunger in the tubing in response to a gas pressure acting on the lower end of the plunger; and passing, while ascending, a liquid from above the body through the upper passage and the liquid cross-hole into an annulus between the body and the tubing.

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates a plunger lift system incorporating a plunger in accordance with one or more aspects of the disclosure.

FIGS. 2 and 3 illustrate a plunger in accordance with one or more aspects of the disclosure.

FIG. 4 is a sectional view of a plunger along the line IV-IV of FIG. 2 illustrating an example of a circumferential and radially extending array of liquid cross-holes in accordance with one or more aspects of the disclosure.

FIG. 5 is a sectional view of a plunger illustrating an example of orientations of one or more liquid cross-holes in accordance with one or more aspects of the disclosure.

FIG. 6 illustrates an example of a pad plunger in accordance with one or more aspects of the disclosure.

FIGS. 7 and 8 illustrate an example of a bypass plunger in accordance to one or more aspects of the disclosure in an open and a closed position.

FIGS. 9 and 10 illustrate another example of a bypass plunger in accordance to one or more aspects of the disclosure in an open and a closed position.

FIGS. 11 and 12 illustrate an example of a two-piece bypass plunger in accordance to one or more aspects of the disclosure in an open and a closed position.

FIGS. 13 and 14 illustrate a plunger in accordance with one or more aspects of the disclosure incorporating a gas cross-hole.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

As used herein, the terms connect, connection, connected, in connection with, and connecting may be used to mean in direct connection with or in connection with via one or more elements. Similarly, the terms couple, coupling, coupled, coupled together, and coupled with may be used to mean directly coupled together or coupled together via one or more elements. Terms such as up, down, top and bottom and other like terms indicating relative positions to a given point or element are may be utilized to more clearly describe some elements. Commonly, these terms relate to a reference point such as the surface from which drilling operations are initiated.

FIG. 1 illustrates a well system 5 incorporating a plunger lift production system 7 which utilizes a plunger, generally denoted by the numeral 10, in accordance to one or more aspects of the disclosure. Plunger 10 includes gas seal arrangement to retard or minimize the migration of gas across the exterior of the plunger during the ascent of the plunger. The gas seal arrangement includes a first seal 12 in the form for example of, and without limitation to, concentric grooves, pads, and/or elastomeric elements located on the exterior circumferential surface 45 of the plunger (e.g., piston, mandrel, body) and the plunger is configured to create a liquid ring 14 about the circumference of the plunger 10 when it is ascending in the well. In FIG. 1 the first seal 12 is illustrated in the form of concentric grooves. Plunger 10 may be a bypass plunger having a central longitudinal fluid passage that is closed toward the bottom end (i.e., gas end) during ascent or a non-bypass plunger.

The well system 5 includes a wellbore 16 extending from a surface 18 of the earth to a producing formation 20. Wellbore 16 may be lined with a casing 22 including perforations proximate the producing formation. The surface end of the casing is closed at the surface by a wellhead generally denoted by the numeral 24. A tubing string 26 having an interior surface 28 extends down the casing and is in connection at the surface with a lubricator 30, also referred to as a catcher, and a production line (conduit) 32. One or more control valves 34 are connected to the tubing string. A spring 36 is positioned at the lower end of the tubing string to stop the downward travel of the plunger 10.

Formation fluid enters the casing through the perforations and into the tubing for example through a standing valve and separates into a liquid 40 portion (with entrained gas) and a gas 42 portion as indicated by the gas-liquid interface 38. The free travelling plunger is lifted from the bottom of the well to the surface to produce a slug of liquid 40 when the lifting gas energy below the plunger is greater than the liquid load and gas pressure above the plunger. In a plunger lift system operation, the well is shut-in by closing a flow control valve for a period of time during which sufficient formation pressure is developed within the casing to move the plunger 10 and the slug of liquid 40 that is above the plunger upward to the surface when the flow control valve is opened.

Dynamic testing conducted in clear tubing with, alternately a spiral plunger, a dart-style plunger and a captured rod plunger determined that the gas escaping up and past the plunger body tends to travel against the wall of the tubing for a nominal distance above and beyond the uppermost end of these plungers. This phenomenon acts to concentrate the heavy liquid located immediately above these plungers into a narrow column around and directly above the fishing neck located at the upper end of each of these plungers. This disclosure teaches plungers that create a seal formed by a ring of liquid (liquid seal or ring 14) about the circumference of the plunger to block or decrease the escape or bypass of gas from below the plunger through the plunger-tubing annulus. Any portion of the gas that is retarded from passing through the annulus and across the plunger is instead directed to act against the lowermost end of the plunger to urge the plunger upward to the surface.

With reference generally to FIGS. 1-14 a liquid 40 (water, crude oil and hydrocarbon condensate), as commonly found within a producing formation 20, has a specific gravity and viscosity greater than hydrocarbon bearing gaseous vapors 42 in the free or pressurized state. The purpose of introducing a ring 14 of one or more of these liquids 40 into the annulus 54 between the exterior of the plunger body and the inner wall 28 of the production tubing 26 of a gas well is to retard the escape of free gas 42 around, up and past the plunger barrier. To that end, the instant disclosure teaches a liquid passage 56 internal to the plunger body 44 and extending axially from a top opening 58 located toward the upper end 46 (e.g., liquid end) of the plunger and one or more liquid cross-holes 60 extending from the axial internal passage 56 to the exterior side surface of the plunger body 44 to recirculate a portion of the liquid 40 that is located above the plunger 10 into the plunger tubing annulus 54 to form the liquid ring 14 to interrupt and prevent the loss of gas 42 from below the plunger to a location above the plunger. As a preponderance of liquid 40 is introduced into the annular space 54 via internal passage 56 and cross-holes 60, the uninterrupted escape of gas 42 is retarded. This retardation is effected by the density of the liquid 40 in comparison to the lighter density of the escaping gas 42. The heavier liquid 40 does not flow upwardly as readily as the escaping gas. Any portion of the upwardly flowing gas stream 42 that is retarded in its escape up the annulus 54 is, instead, directed to act against the lowermost end of the plunger, motivating the plunger upwardly.

FIGS. 2 and 3 illustrate an example of a plunger 10 in accordance to one or more embodiments. Plunger 10 has an elongated body 44 (e.g., piston, mandrel) having a longitudinal axis 8 and extending from a top end 46 to bottom end 48. The plunger includes a first seal 12 on the exterior of the body 44. In this example the first seal, generally denoted by the numeral 12, is formed by a plurality of circumferential grooves 50 spaced longitudinally apart along the outer surface of the body 44. The body 44 has a minor diameter 51 at the grooves 50 and a major diameter 53 at the circumferential ribs 52 located between the grooves 50. In some embodiments, the groove 50 may be a singular groove helically arrayed along the mid length of the plunger body. The depth of the one or more grooves 50 is a tradeoff between the efficiency of a deeper groove versus the desire for a heavier plunger. Heavier plungers fall more rapidly which increases the number of plunger trip cycles that can be completed in a given time-frame. The purpose and function of these one or more grooves 50 is to disturb and interrupt the free passage of the up-flowing gas stream 42 that would otherwise escape via the annulus 54 between the plunger body and inner wall of the tubing. Even in the presence of this plurality of grooves 50, the over-pressure of the gas stream 42 from below the plunger 10 causes at least a minimum amount of gas to slip through the plunger tubing annulus 54 and past the plunger.

The plunger 10 includes an internal passage 56 (e.g., liquid passage) extending axially from the top opening 58 so that the liquid 40 that is located above the plunger can pass into the internal passage and pass through the cross-holes 60 to form the liquid ring 14 (FIG. 3) circumferentially around the plunger body. In FIG. 2 the axial internal passage 56 extends only partially through the body 44 and it is not open at the lower end 48. For example, in FIG. 2 the upper passage 56 terminates at a position 59. The internal liquid passage 56 can be an upper portion of a bypass that has port toward the lower end that can be closed by a valve element to allow the gas pressure below the plunger to act on the plunger and lift the plunger to the surface for example as illustrated in FIGS. 7-12.

The top end of the plunger 10 includes a fishing neck 66 having a surface or profile on which a fishing tool can engage if it is necessary to manually retrieve the plunger from well. The fishing neck 66 may have an external (i.e., male) profile or surface 68 (see, e.g. FIGS. 2-3, 9-10, and 13-14) or an internal (i.e. female) profile or surface 70 (see, e.g. FIGS. 7-8 and 11-12). In accordance to some aspects of the disclosure an internal or female fishing neck profile 70 may be utilized to encourage more liquid to enter the internal passage 56 and to pass through the liquid cross-holes 60 to form the liquid ring 14.

The illustrated plunger 10 has a plurality of liquid cross-holes 60 that extend from the internal axial passage 56 to the exterior side surface 45 (see, e.g. FIGS. 4-5) of the plunger body 44. The liquid cross-holes 60 may be arranged in various axial and circumferential configurations. The plunger may have a single cross-hole 60. During the ascent phase of the plunger cycle, a portion of the liquid 40 above plunger will, by the force of gravity, enter into the internal liquid passage 56 through the top opening 58 and will thereafter radially exit the interior of the plunger body by flowing through the one or more liquid cross-holes 60 and entering into the annulus 54 which is generally occupied by up-flowing gas 42.

The locations and size of the flow path provided by the one or more liquid cross-holes 60 may be a function of the density and viscosity of the liquid 40 to be lifted from the tubing string. A higher viscosity liquid 40 will necessitate a larger flow area through the one or more cross-holes 60. The caution against an abundance of cross-holes 60 at the lower end of the middle section of the plunger is the concern that the liquid 40 introduced into the lower end of the annulus 54 may escape downward and be lost into the lower end of the production tubing string.

The outer diameter of the ribs 52 of the typical spiral plunger is generally only 95 percent of the inner diameter of the tubing 26 based on best practices guidelines within the discipline. When a plunger migrates to one side of the tubing and makes sliding contact with the inner wall of the tubing the annular gap on the opposite side is increased, advancing inefficiency. The liquid cross-holes 60 and discharged liquid 40 can act to centralize the plunger in the tubing string and reduce wear on the plunger and the tubing and/or act to seal the larger annulus side to gas with the liquid seal 14.

One or more liquid cross-holes 60 may be placed within the minor diameter 51 so as to terminate within a groove 50 so the liquid 40 will be directed into groove between the adjacent ribs 52 to promote the liquid 40 encircling the body 44 to form the liquid ring 14. Cross-holes 60 that terminate at the minor diameter are also specifically denoted from time-to-time with the numeral 62. Cross-holes 60 may be positioned to terminate at the major diameter 53, along a rib 52, so that the liquid 40 is deposited or fed directly to the annulus 54 proximate the interface of the major diameter and the inner surface of the tubing. Cross-holes 60 that terminate at the major diameter are also specifically denoted by the numeral 64 from time-to-time. In a self-limiting function, the flow of liquid 40 from any cross-hole 60, 64 at the major diameter 53 that is impinging on the tubing wall will be reduced or blocked and the liquid 40 in the internal passage 56 will be forced to exit the plunger body via a cross-hole 60, 64 that is opposite the blocked cross-hole. By this method, the volume of sealing liquid 40 is directed to the annulus on the side of the plunger 10 where the majority of escaping gas 42 is transiting. A further observation is that the liquid 40 from the blocked cross-hole 60, 64 tends to act on the tubing and urge the plunger away from the tubing wall to a position axial to the tubing. A centralized plunger does not promote excessive wear of the plunger or the tubing.

The liquid cross-holes 60 may be formed in different positions relative to the longitudinal axis 8 and the axial internal passage 56. For example, cross-holes 60 may extend outward from the axial passage 56 and axis 8 at an upward angle (see, e.g. FIGS. 11, 12), a downward angle (see, e.g. FIGS. 7-10 and 13-14) and/or substantially perpendicular to the axial passage 56 (see, e.g., FIGS. 2-3 and 6-14).

It is noted that during the downward fall portion of the plunger cycle, the liquid ring seal 14 does not exist because there is no liquid 40 within the internal passage 56. During the downward travel portion of the typical plunger cycle, the plunger moves through a stationary column of quiescent gas 42. Downwardly angled cross-holes 60 will encourage the uptake of dry gas 42 into passage 56 during the downward travel of the plunger. The downwardly angled liquid cross-holes 60 will not promote inefficiency by leaking gas 42 on the upward travel of the plunger because the cross-holes are employed in disgorging the higher density liquid 40. Those practiced in the art will recognize that a combination of the various cross-hole positions and locations may be advantageous.

With reference FIGS. 1-14 and in particular to FIGS. 4 and 5, the liquid cross-holes 60 may extend radially or tangentially from the axial central passage 56. FIG. 4 illustrates cross-holes 60 that extend radially from the axial passage 56 to the outer side surface 45 of the plunger body 44. FIG. 5 illustrates cross-holes 60 that extend tangentially from the axial passage 56 to the outer side surface 45 of the plunger body 44. A plunger may include a number of cross-holes that extend radially from the axial passage 56 and a number of cross-holes that extend tangentially from the axial central passage. For example, a plunger 10 may include the one or more of the circumferential array of radial cross-holes 60 of FIG. 4 spaced axially apart from a one or more of the tangentially extending liquid cross-holes of FIG. 5. The liquid 40 discharged through the tangentially extending cross-holes 60 act to impart a spin to the plunger during ascent which promotes an even wear pattern on the body 44.

In accordance to some embodiments a plurality of liquid cross-holes 60 are arranged axially and circumferential on the plunger body. In accordance to one or more embodiments at least two liquid cross-holes 60 are positioned substantially on the same horizontal plane, for example a horizontal plane as illustrated in FIGS. 4 and 5, and spaced circumferentially apart. In accordance to one or more embodiments at least three liquid cross-holes are positioned substantially on the same horizontal plane in an array and spaced circumferentially apart. In some embodiments the three arrayed cross-holes 60 are spaced an equal distance, angular distance, from one another. In accordance to one or more embodiments each liquid cross-hole of the three arrayed cross-holes extend radially from the liquid passage and substantially perpendicular to the longitudinal axis. In accordance to some embodiments at least one of the plurality of liquid cross-holes extends tangentially to the liquid passage. As will be understood by those skilled in the art, various configurations of the liquid cross-holes can be arranged to achieve one or more objects disclosed herein including without limitation creating the liquid ring seal 14, inducing spin to the plunger, and centering the plunger in the tubing.

FIG. 6 illustrates an embodiment of a plunger 10 in which the first seal 12 is in the form of pads 72 and is described with reference generally to FIGS. 1-5. The pads 72 are loosely held on the perimeter 45 of the plunger body 44 in a manner that allows for an outward bias of the pads for sealing engagement with the inner wall of the tubing. As the pads 72 make sliding contact with the tubing the natural movement of up-flowing gas past the plunger is retarded and reduced by the pads.

The pad plunger 10 includes an internal passage 56 (e.g., liquid passage) extending axially from the top opening 58 so that the liquid 40 that is located above the plunger can pass into the internal passage and pass through the cross-holes 60 to form the liquid ring 14 (FIG. 3) circumferentially around the plunger body. In FIG. 6 the axial internal passage 56 extends only partially through the body 44 and it is not open at the lower end 48. In accordance to some embodiments the pad plunger 10 may be a bypass plunger where the internal passage 56 extends to a lower opening that is closed with a valve element for the ascent portion of the plunger cycle. A non-limiting example of a bypass plunger is disclosed in U.S. Pat. No. 7,243,730 which is incorporated herein by reference. In U.S. Pat. No. 7,243,730 the valve element to close the bottom opening to the axial passage is shown as a separate element from the plunger body. Other valve elements may be utilized such as disclosed in FIG. 7-10.

The illustrated pad plunger 10 has one or more liquid cross-holes 60 that extend from the internal axial passage 56 to the exterior side surface 45 (see, e.g. FIGS. 4-5) of the plunger body 44. The liquid cross-holes 60 may be arranged in various axial and circumferential configurations. The axial cross-holes may extend perpendicular to the axis or angled upward or downward relative to the plunger axis. The plunger may have a single cross-hole 60. During the ascent phase of the plunger cycle, a portion of the liquid 40 above plunger will, by the force of gravity, enter into the internal liquid passage 56 through the top opening 58 and will thereafter radially exit the interior of the plunger body by flowing through the one or more liquid cross-holes 60 and entering into the annulus 54 which is generally occupied by up-flowing gas 42. In the illustrated embodiment the cross-hole(s) 60 are shown located at a minor diameter 51 and above at least one of the pads 72. Locating the cross-holes above a pad 72 may prevent or mitigate the loss of liquid 40 from the annulus 54 to below the plunger during ascent. The gas 42 pressure and the pad 72 will tend to resist the downward migration of the liquid 40 through the annulus 54.

FIGS. 7-12 illustrate examples of bypass plungers 10 configured to create a liquid ring seal about the circumference of the plunger body. With additional reference to FIGS. 1-6, the internal axial passage 56 in the bypass plungers 10 extends from the top opening 58 toward the top end 46 of the plunger body 44 to a lower opening 76 toward the bottom end 48 (i.e., gas end) of the plunger body 44. The bypass plunger 10 includes a valve element 74 that closes the lower opening 76, or gas port, when the plunger is at the bottom of the tubing so that the gas 42 pressure can act on the lower end of the plunger body and push the plunger and the accumulated liquid 40 in the tubing above the plunger to the surface. FIGS. 7 and 8 illustrate a dart-type plunger, FIGS. 9 and 10 illustrate a captured rod-type plunger, and FIGS. 11 and 12 illustrated a two-piece type of plunger where the valve element 74 is detached from the plunger body when the bypass is open.

The illustrated bypass plungers 10 utilize the common spiral pattern groove 50 for a first form external sealing element 12. As such, each of these bypass plungers can benefit from an improvement of the liquid ring 14 (FIG. 3) sealing means. Because the axial passage 56 extends through the full length of the of the plunger body the cross-holes 60 may be positioned at any point along the length of the bypass plunger. However, it may be desired to position the cross-holes 60 in the upper portion of the middle section to avoid or mitigate the loss of the liquid 40 from the plunger tubing annulus to below the plunger. As noted the gas pressure below the plunger tend to resist the downward migration of liquid 40 through the plunger tubing annulus.

The upper ends 46 of the illustrated dart plunger (FIGS. 7-8) and two-piece plunger (FIGS. 11-12) have internal fishing neck profiles 66, 70 at the top opening 58. The bypass plunger 10 (e.g., captured rod plunger) illustrated in FIGS. 9 and 10 has an external fishing neck profile 66, 68 and the top opening 58 is formed toward the top end 46 and below the fishing neck 66.

FIGS. 13-14 illustrate an additional embodiment of a plunger 10 that further includes a lower axial gas passage 78 and gas cross-holes 82. The plunger 10 of FIGS. 13-14 is described with additional reference to FIGS. 1-12. The plunger 10 of FIGS. 13 and 14 has an external seal 12 such as spiraling groove 50. The plunger includes a gas seal arrangement of an upper axial liquid passage 56 extending axially from the top opening 58 so that the liquid 40 that is located above the plunger can pass into the internal passage and pass through the cross-holes 60 to form the liquid ring 14 (FIG. 14) circumferentially around the plunger body 44. The axial upper liquid passage 56 extends only partially through the body 44 and it is not open at the lower end 48.

As indicated above, it is counter-productive to allow the liquid 40 that is in the tubing 26 above the plunger to pass by the plunger and be loss back in the well below the plunger. The gas 42 pressure below the plunger will tend to resist the downward migration of liquid 40 through the annulus 54. It has been indicated above that to further resist and minimize this loss it may be desired to position the liquid cross-holes 60 a sufficient distance above the lower end 48.

The plunger 10 illustrated in FIGS. 13-14 discloses another mechanism to resist the loss of liquid 40 through the annulus 54 to below the plunger. In this embodiment the plunger 10 includes a lower gas passage 78 extending axially upward from a bottom opening 80 located proximate to the bottom (gas) end 48 of plunger body. The lower axial gas passage 78 terminates at an upper end 79 located inside of the body such that the axial gas passage is not open at the upper end of the plunger and it does not communicate directly with the axial liquid passage 56. The upper axial passage 56 terminates at an end 59 inside of the plunger body and the lower axial gas passage 78 illustrated as terminating at end 79 inside of the plunger body are separated by a plug 84 in this example. The plug 84 may be permanent plug formed for example by a portion of the body 44 or the plug may be removable. One or more gas cross-holes 82 extend from the axial gas passage 78 to the outside diameter of the plunger body to pass gas 42 from below the plunger to the annulus 54 at a location below the liquid ring 14 that is deposited through the liquid cross-holes 60.

As described above with reference to the liquid cross-holes 60, the gas cross-holes 82 may be orientated at any angle relative to the longitudinal axis 8. In FIGS. 13 and 14 on or more gas cross-holes 82 are angled upward. Any gas 42 injected into the annulus 54 at a point below the liquid cross-holes 60 will attempt to rise upwardly within the annulus.

Similar to the liquid cross-holes 60, it may be desired to configure a circumferential array of gas cross-holes 82 open at the major diameter through the ribs 52 to provide a centralizing force to the plunger relative to the tubing. When the gas-delivery cross-holes 82 are circumferentially spaced and positioned at the ribs between the one or more grooves 50 the gas 42 stream is more readily directed against the inner wall of the tubing, acting to centralize the plunger within the tubing string.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded. 

What is claimed is:
 1. A plunger for moving up and down in a tubing string in a plunger lift system, the plunger comprising: an elongated body having an upper end, a lower end and a longitudinal axis; an upper passage extending axially in the body from a top opening located toward the upper end; and a liquid cross-hole extending from the upper passage to an outer circumferential surface of the body.
 2. The plunger of claim 1, wherein the liquid cross-hole extends radially from the upper passage.
 3. The plunger of claim 1, wherein the liquid cross-hole extends tangentially from the upper passage.
 4. The plunger of claim 1, wherein the liquid cross-hole extends substantially perpendicular to the longitudinal axis.
 5. The plunger of claim 1, wherein the liquid cross-hole extends outward from the upper passage at a downward angle.
 6. The plunger of claim 1, wherein the liquid cross-hole extends outward from the upper passage at an upward angle.
 7. The plunger of claim 1, the liquid cross-hole comprises a plurality of liquid cross-holes arranged circumferentially and axially on the body.
 8. The plunger of claim 7, wherein at least one of the plurality of liquid cross-holes extends tangentially from the upper passage.
 9. The plunger of claim 7, wherein at least three liquid cross-holes of the plurality of liquid cross-holes are spaced circumferentially apart along the same horizontal plane.
 10. The plunger of claim 1, wherein the liquid cross-hole comprises an array of liquid cross-holes arranged on the same horizontal plane.
 11. The plunger of claim 10, wherein each liquid cross-hole of the array of liquid cross-holes extends substantially perpendicular to the longitudinal axis.
 12. The plunger of claim 10, wherein at least one liquid cross-hole of the array of liquid cross-holes extends tangentially from the upper passage.
 13. The plunger of claim 10, further comprising an additional liquid cross-hole spaced axially from the array of liquid cross-holes, wherein the additional liquid cross-hole extends tangentially from the upper passage.
 14. The plunger of claim 1, wherein the upper passage extends from the top opening to a terminal end located inside of the body.
 15. The plunger of claim 1, wherein the upper passage extends from the top opening to bottom opening toward the lower end; and further comprising a valve element to selective close the bottom opening.
 16. The plunger of claim 1, further comprising a sealing mechanism located on the outer circumferential surface.
 17. The plunger of claim 16, wherein the sealing mechanism comprises one selected from a circumferential groove and a pad.
 18. A method, comprising: locating a plunger proximate a bottom end of a tubing disposed in a wellbore, the plunger comprising an elongated body having an upper end, a lower end and a longitudinal axis, an upper passage extending axially in the body from a top opening located toward the upper end, and a liquid cross-hole extending from the upper passage to an outer circumferential surface of the body; ascending the plunger in the tubing in response to a gas pressure acting on the lower end of the plunger; and passing, while ascending, a liquid from above the body through the upper passage and the liquid cross-hole into an annulus between the body and the tubing.
 19. The method of claim 18, wherein the liquid cross-hole comprises a plurality of cross-holes positioned circumferentially about the body.
 20. The method of claim 18, wherein the body comprises one or more circumferential grooves on the outer circumferential surface. 